During TMS planning and stimulation it is desired to induce the minimum effective dose of stimulation at any given place in the brain. By giving a dose which is lower than the minimum effective dose it is likely that the dose will not have the intended effect. By giving a dose which is much larger than the minimum effective dose has multiple side effects. Examples of some are the over stimulation of an area, the stimulation of a larger area than intended, the accumulation of excess dose in an area or region which limits the length of a stimulation session, the overheating of an area of the brain and the possibility of seizures.
It is possible to experimentally determine the minimum effective dose for certain areas of the brain, e.g. within the motor cortex, where the effect of the stimulation can be measured or observed. It is typical to then use that minimum effective dose as a guideline for other areas of the brain, either replicating that dose or increasing that dose by a predetermined amount, e.g. stimulating another region with 120% of the minimum effective dose for the other region. Typically, general rules of thumb are applied and there is no correlation between the dose which is administered and the actual minimum effective dose for each non-measurable location.
One of the key features of how effective a dose will be is the neural structure of the area to be stimulated and the relative orientation of an induced electric field to that area. Currently, TMS and nTMS systems do not take into account this information, resulting in inefficient and ineffective doses of stimulation being applied. It is therefore a desire to have a system and method which accounts for the neural structure at a stimulation location in order to determine a minimum effective dose and/or orientation. Additionally, it is desirable to understand the actually effectiveness of a dose at a location in or on the brain which is not easily measurable.